1. Field of the Invention
The present invention relates to an optical fiber communication method, and, more particularly, to an optical fiber communication method using optical wavelength multiplexing and a multimedia optical fiber network using the same.
2. Related Arts
Recently, information subjected to the communication in offices has been varied significantly. For example, various signals are used in a mixed manner in offices, the signals being data signals in computers and work stations, still-image signals in facsimiles, voice signals of telephones, and image signals of video conference systems. However, each of the signals is arranged to be transmitted at an individual transmission speed and to have an individual transmissible capacity and the continuity. On the other hand, information to be transmitted has been needed to have a large capacity and to correspond to a high speed transmission since the terminal equipments which use the information have been in a trend toward high performance. In accordance with the rapid progress of the information-oriented society, networks have been needed to have performance enabling to transmit signals each having individual transmission speed, transmissible capacity, and continuity through the same transmission medium, that is, performance to correspond to multimedia and high speed processing is needed. To this end, optical fiber networks have been employed recently as a preferred network which can meet the desires. In this description, the difference in the signal continuity means the difference between signals (to be called "continuous signals" hereinafter) such as voice signals and video signals which cannot be interrupted during the transmission and signals (to be called "data signals" hereinafter) such as data for computers which does not arise any problem even if they are transmitted with interruptions interposed.
In general, a carrier sense multiple access/collision detection (to be abbreviated to "CSMA/CD" hereinafter) system, a token passing system, and a time division multiple access (to be abbreviated to "TDMA") system are available as the signal access system for the optical fiber network. The TDMA is usually employed in order to correspond to multimedia. The reason for this lies in that the CSMA/CD and the token passing are originally arranged to be used in a packet switched communication which is suitable for transmitting data signals, causing a complicated means (a priority-addition means or delay-prevention means) to be provided for the packet control in order to maintain the continuity of the signals at the receipt terminals when signals such as voice signals and video signals which are necessary to have continuity are processed. Furthermore, the CSMA/CD and the token passing involve a large number of limitations.
On the other hand, the TDMA is an access arranged such that a signal from each of the terminal equipments is allotted to the time slot in the frame so as to be compressed on the time axis. Therefore, continuous signals can be readily treated and the limitations can be reduced. Although there are various systems classified on the basis of the way of allotting the time slots, a variable allocation system is widely used, the variable allocation system being arranged such that the time slots are allotted to each of the terminal equipments by a control unit of the network. As a method to correspond to multimedia using the TDMA, there is a method that is arranged such that a portion of the time slots in the frame are allotted to the packet switching which is capable of transmitting burst signals, the remainder being then allotted to the line switching which is capable of transmitting continuous signals.
However, the optical network using the TDMA and capable of corresponding multimedia encounters the following problems: since the TDMA multiplexes the signal from each of the terminal equipments in a time sequential manner, that is, it compresses the signals on the time axis, the transmission speed on the network becomes higher than that of the signal to be transmitted from each of the terminal equipments and a limitation arises that a signal having individual speed from each of the terminals needs to be converted into the same transmission speed before the signals are transmitted to the network. That is, the transmission speed on the network is necessary to be the product of speed at the terminal which displays the highest transmission speed and the number of the multiplexings assumed for the terminal. Furthermore, the terminal displaying the lowest transmission speed is needed to time-compress the signal to the transmission speed on the network before the signal transmission.
Assuming that a multimedia network is established by substantially 10 terminals each of which is arranged to be a transmission speed of several tens of kbps and substantially 10 terminals each of which is arranged to be a transmission speed of several hundred Mbps, a transmission speed of several Gbps is necessary for the network to be established. Furthermore, the terminals each of which is arranged to be the transmission speed of several tens of Kbps are respectively necessary to be provided with a communication device for the purpose of time-compressing the signal to the transmission speed on the network, that is, to several Gbps.
However, it is difficult in terms of the technical viewpoint to establish the network arranged to be the transmission speed of the above-described level. If it can be established, the cost becomes excessive. Furthermore, the low speed terminals whose cost needs to be reduced are necessary to be respectively provided with a high speed communication system which is an expensive device for the purpose of establishing a connection with the network, causing the establishment of the network to become impossible. In addition, the TDMA system in which the above-described complicated control is necessary is needed to be provided with a unit for controlling the network. Therefore, such a system is disadvantageous in terms of the cost, and a problem of limitation of the capability of extensibility also arises.